The great whales, once under the threat of death from most seafaring nations (and now only a scant few), are some of the largest creatures to ever grace our planet. The group includes all the aptly named Mysteceti, the whales who filter plankton and krill through the plates of baleen that line their jaws, and the legendary sperm whales familiar to all high school students thanks to Moby Dick.

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Over the thousand years of widespread whaling, we wiped out between two thirds and 90 percent of great whale populations, according to some estimates. The planet's total whale biomass may have been reduced by as much as 85 percent. Some species fared worse than others: blue whales were reduced to just 1 percent of their historical numbers in the Southern Hemisphere.

In a recent paper in the journal Frontiers in Ecology and the Environment, ecological economist Joe Roman and colleagues described four ways in which whales are vital to ocean health and to the future of our increasingly hot planet.

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Whales Are Predators

The fact that whales can consume a ton (literally!) of food actually helps keep carbon under the ocean rather than in the atmosphere, slowly cooking the Earth under a warm blanket of greenhouse gas. Here's why.

The amount of food required to allow just one blue whale to survive is enough to feed seven minke whales or 1500 penguins. Indeed, when whales declined, other species like penguins and Antarctic fur seals enjoyed a baby boom since there was suddenly so much more food for them to eat. But despite the ability of 1500 penguins to eat the same food as a single blue whale, their biomass is only 8% of the whale.

The greater biomass of the blue whales allows marine ecosystems to store more carbon simply because the animals – and their carcasses, once they die – are larger. In other words, for the same amount of food, the great whales allow the oceans to retain a larger amount of carbon than smaller animals ever could.

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Whales Are Prey

Whales are big, and the great whales are the biggest, but that doesn't provide them with protection from all forms of predation. Because they are so large, a single whale represents a bounty in energy and resources for any creature large, powerful, or stubborn enough to hunt it. Fossils provide evidence that the ancient (and very much extinct) shark Megalodon hunted the great whales, and both historical and modern accounts verify that the smaller killer whales do the same. The high frequency of scrapes and rake marks on the flukes of most large whale species," writes Roman, "affirm[s] a long-standing and wide-spread utilization of whales as prey."

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When killer whales were forced to find other sources of energy, many turned to smaller marine mammals, like seals, sea lions, and sea otters. The loss of sea otters meant that their primary source of food, sea urchins, were suddenly without a significant predation pressure of their own. Sea urchin populations in the northern Pacific ocean flourished, and as a result, the kelp forests that they rely on for food began to decline.

The decline of kelp forests not only substantially changed the local ecosystems both in terms of biodiversity and biomass, but also reduced the ability of those marine ecosystems to retain carbon. Just like terrestrial forests, kelp forests are an important carbon sink, a manner in which it can be sequestered away from the atmosphere. But as kelp forests lost their vigor, they also lost their ability to hold onto carbon.

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Whales Pee and Poo

Everybody does it, but whales take it seriously. Whales and other marine mammals find food deep in the water – sperm whales dive to the darkest, deepest seas to find squid – but then return to the surface to eject their waste. And they do it in the most magnificent way possible, releasing massive amounts of nitrogen and iron into the water by way of fecal plumes. That allows for the growth of phytoplankton near the ocean surface. Eventually, those phytoplankton blooms sink, transferring at least 200 thousand tons of carbon each year from the atmosphere to the deep sea.

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Whales don't only travel over vast distances in depth; they also migrate horzontally across the planet's surface. Baleen whales have some of the largest migrations in the world, moving from feeding at higher latitudes and calving at lower latitudes. While they fast during lactation, females release all the nitrogen that they stored up in their body fat as they burn it to maintain their energy. Thus, according to one estimate, blue whales transport 88 tons of nitrogen each year from their high latitude feeding grounds near Alaska or Antarctica to their low latitude birthing grounds in the tropics.

Calculating backwards, before commercial whaling began, that figure would have been closer to 24 thousand tons of nitrogen. That would have allowed phytoplankton to blossom, and that would have provided sequestration for an additional 140 thousand tons of carbon each year.

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Roman calls the transfer of nutrients and chemicals by whales the "whale pump" and "great whale conveyor belt," to describe the vertical and horizontal gradients, respectively. As whale populations recover, he writes, those processes may allow our oceans to slowly begin acting as Earth's massive carbon sink, once again.

Whales Are But Mere Mortals

Whales may be magnificant creatures, but they eventually die. Because they're made mostly of proteins and lipids, dead whales provide brief feasts for deep sea dwellers in a place that is largely void of nutrients and energy. After a 40-ton grey whale takes its last breath, it sinks silently down, bringing some 2 million grams of carbon along with it. Altogether, whale falls currently transfer some 190 thousand tons of carbon each year from the atmosphere to the deep sea.

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But that's an estimate based on today's whale populations, which have only begun to recover. If great whale populations were restored to their pre-whaling sizes, the increase in carbon export would be "comparable in magnitude to the hypothetical [climate engineering] projects intended to mitigate climate change," argues Roman. Whale conservation would accomplish the same in terms of carbon sequestration as the iron or nitrogen fertilization projects, which the IPCC described in 2007 as "speculative" and "without a clear institutional framework for implementation," aim to accomplish.

Does It Matter?

Whales provide many more ecosystem services beyond their role in global carbon transfer. Indeed, Roman and colleagues acknowledge that the contribution of whales to global carbon fluxes is indeed relatively small compared to other processes. Still, a continued effort towards whale conservation "may help to buffer marine ecosystems from destabilizing stresses," he says.

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When you remove large predators en masse from their habitats, bad things tend to happen. When wolves were driven out of Yellowstone, the elk population exploded because they were no longer supressed by wolf depredation. But more elk meant that the plants they ate suffered. And the bears, beavers, and bison, who relied on many of the same plants as the elk, suddenly found themselves without enough food to eat. The entire Yellowstone ecosystem had shifted. But then wolves were re-introduced. The food chain began to settle into its former equilibrium. Elk populations were kept in check. Beaver and bison numbers increased. Where wolves were once thought primarily as nuisance animals (and in many cases, still are), conservationists, researchers, and policymakers are increasingly recognizing them for the ecosystem services that they provide.

Similarly, whales were once thought of in terms of the myriad ways in which they entered the consumer marketplace. From the harvest of great whales came meat, oil, whalebone, and spermaceti, a waxy substance found in the heads of sperm whales that was used in candles, ointments, and as a lubricant. But now, they are becoming increasingly recognized for the ecosystem services that they provide. And it's only now, after having begun to recover from a millennium of whaling, that scientists have even been able to notice. Only now can they begin to empirically quantify just how integral whales are to the health of ocean ecosystems.